During the past few years, increasing emphasis has been placed on the behavioral and mood disorders which accompany the human menstrual cycle. A variety of eating disorders are also associated with changes in blood hormone levels, but identification of the hormonal contributions has been difficult to assess. The female rodent has a clearly defined reproductive (estrous) cycle which is well characterized and during which changes in eating behavior has been reported. Of special relevance to these changes are the effects of gonadal hormones on central nervous system transmitters such as serotonin and norepinephrine. Both neurotransmitters have been implicated in the regulation of neuroendocrine activity and sexual behavior in the female rodent. Although these neurotransmitters influence total food intake, they may have a particular effect on the ingestion of carbohydrates. The proposed studies are directed at more clearly identifying the relation between the effect of gonadal hormones on neurotransmitters, eating behavior, and carbohydrate intake, intact and ovariectomized female rats will be monitored for their selection of carbohydrate, protein or fat during the estrous cycle or following hormone replacement. Serotonin and norepinephrine levels precursors and metabolites will be examined in brain tissue and in blood. These studies are particularly relevant to the claim that carbohydrate craving varies during the human menstrual cycle. It is hoped that these studies can serve as a model approach for identifying the hormonal mechanisms which may be responsible for human eating disorders.